Question 1

Explain how α and β units differ in their structure and function for voltage-activated sodium channels versus nAChRs?

Accepted Answer

The subunit effectively forms the entire voltage-activated sodium channel, including all of its transmembrane domains, poor-forming region, and its voltage sensor that gates (opens) the channel. By contrast the submit forms just one-fifth of the nAChR (even in a homo-pentameric channel made of 5 α-subunits, any single α-subunit forms one-fifth of the receptor). The α-subunit of the nAChR binds the ligand for nAChRs, but the α-subunit of voltage-activated channels has no equivalent ligand-binding role. β-subunits also make up one-fifth of the nAChR; they occupy nearly the same size as α-subunits and play a similar role in the channel apart from ligand-binding β-subunits in voltage-activated sodium channels are much smaller than the subunit and play an auxiliary role.

Question 2

Which modifications reduce receptor conductance?

Accepted Answer

A)  substitution of 2′ threonine (T) with a smaller hydrophilic residue 
B)  substitution of 2′ threonine (T) with a larger hydrophilic residue 
C)  substitution of 2′ threonine (T) with a smaller hydrophobic residue 
D)  substitution of 2′ threonine (T) with any polar residue 
E)  substitution of 2′ threonine (T) with a larger hydrophobic residue 
A)  substitution of 2′ threonine (T) with a smaller hydrophilic residue 
B)  substitution of 2′ threonine (T) with a larger hydrophilic residue 
C)  substitution of 2′ threonine (T) with a smaller hydrophobic residue 
D)  substitution of 2′ threonine (T) with any polar residue 
E)  substitution of 2′ threonine (T) with a larger hydrophobic residue E

Question 3

Which structural property is common among glutamate receptors and KCS potassium channels?

Accepted Answer

A)  Ion selectivity of the pore 
B)  The number of transmembrane segments that comprise the receptor/channel 
C)  A small helical region between transmembrane segments that forms the pore 
D)  Positively charged amino acids located at every third position in one of the transmembrane domains 
E)  The pore region located on the cytoplasmic side of the receptor/channel 
A)  Ion selectivity of the pore 
B)  The number of transmembrane segments that comprise the receptor/channel 
C)  A small helical region between transmembrane segments that forms the pore 
D)  Positively charged amino acids located at every third position in one of the transmembrane domains 
E)  The pore region located on the cytoplasmic side of the receptor/channel C

Question 4

Why do we refer to the nAChR as a receptor rather than a channel?

Accepted Answer

A)  To distinguish it from muscarinic receptors, which do not form a channel 
B)  Because it is present in skeletal muscle and electric organs (a modified form of muscle) as well as neurons 
C)  Because its principal function is reception of signals from presynaptic partners 
D)  To emphasize its commonality with other Cys-loop receptors and dissimilarity compared to voltage-activated ion channels 
E)  Because its ligand-binding properties more substantively contributed to its characterization than the conduction properties of its channel 
A)  To distinguish it from muscarinic receptors, which do not form a channel 
B)  Because it is present in skeletal muscle and electric organs (a modified form of muscle) as well as neurons 
C)  Because its principal function is reception of signals from presynaptic partners 
D)  To emphasize its commonality with other Cys-loop receptors and dissimilarity compared to voltage-activated ion channels 
E)  Because its ligand-binding properties more substantively contributed to its characterization than the conduction properties of its channel

Question 5

Which of the following is an invertebrate anion channel?

Accepted Answer

A)  MOD-1 receptor 
B)  EXP-1 receptor 
C)  GluCl receptor 
D)  GABAA receptor 
E)  Glycine receptor 
A)  MOD-1 receptor 
B)  EXP-1 receptor 
C)  GluCl receptor 
D)  GABAA receptor 
E)  Glycine receptor

Question 6

Modifying the primary structure of a receptor encapsulates which of the following techniques?

Accepted Answer

A)  Site-directed mutagenesis 
B)  Receptor expression in Xenopus oocytes 
C)  Electrical recording of single-channel or whole-cell receptor currents 
D)  Ligand binding affinity and pharmacology 
E)  Replacement of polar amino acids with nonpolar ones 
A)  Site-directed mutagenesis 
B)  Receptor expression in Xenopus oocytes 
C)  Electrical recording of single-channel or whole-cell receptor currents 
D)  Ligand binding affinity and pharmacology 
E)  Replacement of polar amino acids with nonpolar ones

Question 7

Which statement summarizes how the 0.3 nm selectivity filter of KCS channels enables potassium to penetrate but not sodium or lithium?

Accepted Answer

A)  Because of their smaller diameter and charge, sodium and lithium ions interact strongly with carbonyl oxygens and effectively get stuck in the pore region and do not flow through the channel. 
B)  Because their diameters exceed 0.3 nm, sodium and lithium are excluded on the basis of size. 
C)  Carbonyl oxygens provide a surrogate environment that keeps potassium ions in aqueous solution while passing through the channel. 
D)  Carbonyl oxygens provide a surrogate environment for dehydrated potassium ions in the selectivity filter that mimics the hydration energy of ions in solution. 
E)  Carbonyl oxygens provide a surrogate environment for dehydrated sodium or lithium ions in the selectivity filter that mimics the hydration energy of ions in solution. 
A)  Because of their smaller diameter and charge, sodium and lithium ions interact strongly with carbonyl oxygens and effectively get stuck in the pore region and do not flow through the channel. 
B)  Because their diameters exceed 0.3 nm, sodium and lithium are excluded on the basis of size. 
C)  Carbonyl oxygens provide a surrogate environment that keeps potassium ions in aqueous solution while passing through the channel. 
D)  Carbonyl oxygens provide a surrogate environment for dehydrated potassium ions in the selectivity filter that mimics the hydration energy of ions in solution. 
E)  Carbonyl oxygens provide a surrogate environment for dehydrated sodium or lithium ions in the selectivity filter that mimics the hydration energy of ions in solution.

Question 8

Imagine that you discover a new brain nucleus and its constituent neurons excite their downstream postsynaptic neighbors. Which of the following receptors are most likely to be expressed by the postsynaptic neighbors?

Accepted Answer

A)  Nicotinic ACh receptors 
B)  Serotonin (5-HT3) receptors 
C)  γ-aminobutyric acid (GABA
A)  receptors 
D)  Glycine receptors 
E)  AMPA receptors 
A)  Nicotinic ACh receptors 
B)  Serotonin (5-HT3) receptors 
C)  γ-aminobutyric acid (GABA
A)  receptors 
D)  Glycine receptors 
E)  AMPA receptors

Question 9

Hydrophobicity of amino acid residues informs which property of nAChRs?

Accepted Answer

A)  Their primary structure, i.e., amino acid sequence 
B)  Secondary and tertiary structure: membrane insertion of alpha helices 
C)  Secondary and tertiary structure: configuration of intracellular loops 
D)  Secondary and tertiary structure: ligand-binding site(s) 
E)  Quaternary structure: arrangement of subunits 
A)  Their primary structure, i.e., amino acid sequence 
B)  Secondary and tertiary structure: membrane insertion of alpha helices 
C)  Secondary and tertiary structure: configuration of intracellular loops 
D)  Secondary and tertiary structure: ligand-binding site(s) 
E)  Quaternary structure: arrangement of subunits

Question 10

What is the principal mechanism of inactivation in voltage-activated channels?

Accepted Answer

A)  Occlusion by elements of the ion channel that do not lie within the membrane 
B)  S6 helix closing off the cytoplasmic mouth of the channel 
C)  Displacement of S4 back to its "resting" position within the membrane 
D)  Inactivation, or current "switching off," of the P-loop, possibly involving the selectivity filter 
E)  Displacement f S6 back to its "resting" position within the membrane 
A)  Occlusion by elements of the ion channel that do not lie within the membrane 
B)  S6 helix closing off the cytoplasmic mouth of the channel 
C)  Displacement of S4 back to its "resting" position within the membrane 
D)  Inactivation, or current "switching off," of the P-loop, possibly involving the selectivity filter 
E)  Displacement f S6 back to its "resting" position within the membrane

Question 11

If we consider Cys-loop and voltage-activated channels as having three main parts: (1) an extracellular portion, (2) an intramembranous portion, and (3) an intracellular portion; then, provide a general functional attribute for each region and how it functions in both Cys-loop and voltage-activated channels.

Accepted Answer

The extracellular portion of Cys-loop an

Question 12

A nicotinic acetylcholine receptor is activated by

Accepted Answer

A)  ACh. 
B)  muscarine. 
C)  intracellular messenger systems. 
D)  -bungarotoxin. 
E)  serotonin. 
A)  ACh. 
B)  muscarine. 
C)  intracellular messenger systems. 
D)  -bungarotoxin. 
E)  serotonin.

Question 13

Ion selectivity of Cys-loop and voltage-activated ion channels depends

Accepted Answer

A)  inversely on the number of subunits (i.e., fewer subunits means higher ion specificity). 
B)  directly on the number of subunits (i.e., more subunits means higher ion specificity). 
C)  on properly spaced charged amino acids in the primary structure of the channel proteins. 
D)  on auxiliary subunits (e.g., β-subunits), which associate with the main (α) subunit of the channel. 
E)  on the P-loop. 
A)  inversely on the number of subunits (i.e., fewer subunits means higher ion specificity). 
B)  directly on the number of subunits (i.e., more subunits means higher ion specificity). 
C)  on properly spaced charged amino acids in the primary structure of the channel proteins. 
D)  on auxiliary subunits (e.g., β-subunits), which associate with the main (α) subunit of the channel. 
E)  on the P-loop.

Question 14

Which of the following factors gates present at the cytoplasmic side of the channel gates outward current flow in Kir channels?

Accepted Answer

A)  β-subunits 
B)  A relatively long carboxy tail that inactivates the channel like in voltage-activated sodium channels 
C)  Calcium 
D)  Magnesium 
E)  Intracellular biochemical messengers 
A)  β-subunits 
B)  A relatively long carboxy tail that inactivates the channel like in voltage-activated sodium channels 
C)  Calcium 
D)  Magnesium 
E)  Intracellular biochemical messengers

Question 15

Describe the conceptually different functional roles for Piezo 1 and Piezo 2 in sensory function?

Accepted Answer

Piezo 1 channels are tasked with detecti

Question 16

A sequence of 24 hydrophobic amino acids at the amino tail of the nAChR subunit ensures

Accepted Answer

A)  that ligand binding occurs principally on the α-subunit (and not β, γ, or δ). 
B)  M1-M4 transmembrane domains align in parallel. 
C)  that nAChRs can dimerize. 
D)  that the first transmembrane domain (M1) forms an helix as required for intercalation in the membrane. 
E)  that ligand-binding sites reside extracellularly. 
A)  that ligand binding occurs principally on the α-subunit (and not β, γ, or δ). 
B)  M1-M4 transmembrane domains align in parallel. 
C)  that nAChRs can dimerize. 
D)  that the first transmembrane domain (M1) forms an helix as required for intercalation in the membrane. 
E)  that ligand-binding sites reside extracellularly.

Question 17

Opening a voltage-gated channel generally involves which of the following roles for S6?

Accepted Answer

A)  Forming the ion selectivity filter in combination with S5 and the S5-S6 linker region 
B)  Sensing transmembrane depolarization via its positively charged amino acids 
C)  Relieving the physical constraints that block the cytoplasmic mouth of the channel 
D)  Displacement within in the membrane via interactions with voltage-detecting S4 
E)  Possibly none: a large body of evidence shows that activation of channel currents can occur independently of an S4-coupled gating mechanism, which casts doubt on the role of S6, too 
A)  Forming the ion selectivity filter in combination with S5 and the S5-S6 linker region 
B)  Sensing transmembrane depolarization via its positively charged amino acids 
C)  Relieving the physical constraints that block the cytoplasmic mouth of the channel 
D)  Displacement within in the membrane via interactions with voltage-detecting S4 
E)  Possibly none: a large body of evidence shows that activation of channel currents can occur independently of an S4-coupled gating mechanism, which casts doubt on the role of S6, too

Question 18

Make an argument that TMC in cochlear hair cells is an ion channel.

Accepted Answer

Examining the amino acid sequence of TMC

Question 19

Which of the following characteristics are similar for voltage-activated sodium channels and voltage-activated calcium channels?

Accepted Answer

A)  Selectivity of their pore regions 
B)  Voltage sensitivity and persistence of activation 
C)  Their position and function of their associated β-subunits 
D)  Prevalence of glycosylation sites in functional channels 
E)  The primary sequence similarity of their α-subunit and equivalent structure of domains I-IV 
A)  Selectivity of their pore regions 
B)  Voltage sensitivity and persistence of activation 
C)  Their position and function of their associated β-subunits 
D)  Prevalence of glycosylation sites in functional channels 
E)  The primary sequence similarity of their α-subunit and equivalent structure of domains I-IV

Question 20

Why was the electric organ of the ray Torpedo key in the structural characterization of nAChRs?

Accepted Answer

A)  It provided sufficient quantities for biochemical isolation of the receptor. 
B)  Its receptors have unique affinity for α-bungarotoxin. 
C)  Compared to vertebrates, Torpedo receptors have a greater diversity of subunits that comprise the receptor and thus provide a wider spectrum of possible tertiary structures. 
D)  Its receptors are uniquely nicotinic whereas vertebrate receptors which can be nicotinic or muscarinic. 
E)  The tertiary structure of its subunits is equivalent to that of vertebrate receptors. 
A)  It provided sufficient quantities for biochemical isolation of the receptor. 
B)  Its receptors have unique affinity for α-bungarotoxin. 
C)  Compared to vertebrates, Torpedo receptors have a greater diversity of subunits that comprise the receptor and thus provide a wider spectrum of possible tertiary structures. 
D)  Its receptors are uniquely nicotinic whereas vertebrate receptors which can be nicotinic or muscarinic. 
E)  The tertiary structure of its subunits is equivalent to that of vertebrate receptors.

Exam 5: Structure of Ion Channels

Explain how α and β units differ in their structure and function for voltage-activated sodium channels versus nAChRs?

Which modifications reduce receptor conductance?

Which structural property is common among glutamate receptors and KCS potassium channels?

Why do we refer to the nAChR as a receptor rather than a channel?

Which of the following is an invertebrate anion channel?

Modifying the primary structure of a receptor encapsulates which of the following techniques?

Which statement summarizes how the 0.3 nm selectivity filter of KCS channels enables potassium to penetrate but not sodium or lithium?

Imagine that you discover a new brain nucleus and its constituent neurons excite their downstream postsynaptic neighbors. Which of the following receptors are most likely to be expressed by the postsynaptic neighbors?

Hydrophobicity of amino acid residues informs which property of nAChRs?

What is the principal mechanism of inactivation in voltage-activated channels?

A nicotinic acetylcholine receptor is activated by

Ion selectivity of Cys-loop and voltage-activated ion channels depends

Which of the following factors gates present at the cytoplasmic side of the channel gates outward current flow in Kir channels?

Describe the conceptually different functional roles for Piezo 1 and Piezo 2 in sensory function?

A sequence of 24 hydrophobic amino acids at the amino tail of the nAChR subunit ensures

Opening a voltage-gated channel generally involves which of the following roles for S6?

Make an argument that TMC in cochlear hair cells is an ion channel.

Which of the following characteristics are similar for voltage-activated sodium channels and voltage-activated calcium channels?

Why was the electric organ of the ray Torpedo key in the structural characterization of nAChRs?

Principles of Signaling and Organization

Signaling in the Visual System

Functional Architecture of the Visual Cortex

Ion Channels and Signaling

Ionic Basis of the Resting Potential

Ionic Basis of the Action Potential

Electrical Signaling in Neurons

Ion Transport Across Cell Membranes

Properties and Functions of Neuroglial Cells

Mechanisms of Direct Synaptic Transmission

Indirect Mechanisms of Synaptic Transmission

Release of Neurotransmitters

Neurotransmitters in the Central Nervous System

Transmitter Synthesis, Storage, Transport, and Inactivation

Synaptic Plasticity

The Molecular and Cellular Biology of Synaptic Plasticity

Mechanisms of Extrasynaptic Communication

Autonomic Nervous System

Walking, Flying, and Swimming: Cellular Mechanisms of Sensorimotor Behavior in Invertebrates

Sensory Transduction

Transduction and Transmission in the Retina

Touch, Pain, and Texture Sensation

Auditory and Vestibular Sensation

Constructing Perception

Initiation and Control of Coordinated Muscular Movements

Development of the Nervous System

Critical Periods in Sensory Systems

Regeneration and Repair of Synaptic Connections After Injury

Appendix

Filters

Which structural property is common among glutamate receptors and K_CS potassium channels?

Which statement summarizes how the 0.3 nm selectivity filter of K_CS channels enables potassium to penetrate but not sodium or lithium?

Which of the following factors gates present at the cytoplasmic side of the channel gates outward current flow in K_ir channels?